Explain the coagulation and flocculation process in water treatment.

Coagulation neutralizes the negative charge on colloidal particles using coagulants like alum, ferric chloride, or polyelectrolytes, allowing particles to aggregate. This occurs in rapid mix chambers with high velocity gradients (>300/s) for 30-60 seconds. Flocculation follows in slow mix basins with gentle stirring (G = 20-75/s) for 20-45 minutes, forming larger settleable flocs. Optimal coagulant dose is determined by jar tests. pH, temperature, and turbidity affect efficiency.